US8107001B2ActiveUtilityA1
Image forming optical system and electronic image pickup apparatus using the same
Est. expiryDec 25, 2028(~2.5 yrs left)· nominal 20-yr term from priority
Inventors:Takayuki Mimura
G02B 15/144113
39
PatentIndex Score
0
Cited by
6
References
7
Claims
Abstract
An image forming optical system includes in order from an object side to an image surface, a first lens group having a positive refracting power, a second lens group having a negative refracting power, and a third lens group having a positive refracting power. At the time of zooming from a wide angle end to a telephoto end, a distance between the first lens group and the second lens group increases, and a distance between the second lens group and the third lens group decreases. The first lens group has a cemented lens which includes a first lens element E 1 , a second lens element E 2 , and a third lens element E 3 . In the cemented lens, the first lens element E 1 is cemented to a surface on one side of the second lens element E 2 , and the third lens element E 3 is cemented to another surface of the second lens element E 2 . The first lens element E 1 is a negative lens, and the second lens element E 2 is a positive lens. The image forming optical system satisfies predetermined conditional expressions.
Claims
exact text as granted — not AI-modified1. An image forming optical system comprising in order from an object side to an image surface;
a first lens group having a positive refracting power;
a second lens group having a negative refracting power; and
a third lens group having a positive refracting power, wherein
at the time of zooming from a wide angle end to a telephoto end, a distance between the first lens group and the second lens group increases, and a distance between the second lens group and the third lens group decreases, and
the first lens group has a cemented lens which includes a first lens element E 1 , a second lens element E 2 , and a third lens element E 3 , and
in the cemented lens, the first lens element E 1 is cemented to a surface on one side of the second lens element E 2 , and the third lens element E 3 is cemented to another surface of the second lens element E 2 , and
the first lens element E 1 is a negative lens, and the second lens element E 2 is a positive lens, and
the image forming optical system satisfies the following conditional expressions (1), (2), (3), and (4)
20 <|νeff−ν 3|<80 (1)
0 <|θgFeff−θgF 3|<0.10 (2)
0.5<θgF2<0.9 (3)
1.2<( fG 1+0.7 ft)/ enz< 5 (4)
where,
ν 1 , ν 2 , and ν 3 denote Abbe's number for the first lens element E 1 , the second lens element E 2 , and the third lens element E 3 respectively,
fE 1 and fE 2 denote focal length of the first lens element E 1 and the second lens element E 2 respectively,
f double denotes a combined focal length of the cemented lens when a boundary surface on an image surface side of the second lens element E 2 is air,
θgF 1 denotes a partial dispersion ratio (ng 1 −nF 1 )/(nF 1 −nC 1 ) of the first lens element E 1 ,
θgF 2 denotes a partial dispersion ratio (ng 2 −nF 2 )/(nF 2 −nC 2 ) of the second lens element E 2 ,
θgF 3 denotes a partial dispersion ratio (ng 3 −nF 3 )/(nF 3 −nC 3 ) of the third lens element E 3 ,
nC 1 , nF 1 , and ng 1 denote a refractive index of the first lens element E 1 for a C-line, an F-line, and a g-line respectively,
nC 2 , nF 2 , and ng 2 denote a refractive index of the second lens element E 2 for the C-line, the F-line, and the g-line respectively,
nC 3 , nF 3 , and ng 3 denote a refractive index of the third lens element E 3 for the C-line, the F-line, and the g-line respectively,
ν deff and θgFeff denote equivalent Abbe's number and equivalent partial dispersion ratio respectively when the cemented lens includes only the first lens element E 1 and the second lens element E 2 , and are expressed by the following expressions
v
deff
=
1
f
t
·
(
ϕ
1
v
1
+
ϕ
2
v
2
)
=
v
1
·
v
2
a
·
v
2
+
(
1
-
a
)
·
v
1
θ
gFeff
=
f
double
·
v
e
(
θ
gF
1
v
1
·
ϕ
1
+
θ
gF
2
v
2
·
ϕ
2
)
=
ve
(
a
·
v
2
·
θ
gF
1
+
(
1
-
a
)
·
v
1
·
θ
gF
2
v
1
·
v
2
)
where
,
a
=
ϕ1
ϕ1
+
ϕ2
ϕ1
=
1
fE
1
ϕ
2
=
1
fE
2
where,
fG 1 denotes a focal length of the first lens group,
ft denotes a focal length at the telephoto end of the image forming optical system, and
enz denotes a distance from a first lens surface of the image forming optical system up to an entrance-pupil position.
2. The image forming optical system according to claim 1 , wherein the image forming optical system satisfies the following conditional expression (5)
2.5 <fE 2/ fG 1<3.0 (5)
where,
fG 1 denotes the focal length of the first lens group, and
fE 2 denotes a focal length of the second lens element.
3. The image forming optical system according to claim 1 , wherein
each of the first lens element E 1 , the second lens element E 2 , and the third lens element E 3 has a positive refracting power, and
the cemented lens includes the first lens element E 1 , the second lens element E 2 , and the third lens element E 3 , and
the first lens group includes a single lens having a positive refracting power, and the cemented lens.
4. The image forming optical system according to claim 1 , wherein
the first lens group includes a single lens having a positive refracting power, and
the single lens having a positive refracting power is disposed on an object side than the cemented lens.
5. The image forming optical system according to claim 4 , wherein the image forming optical system satisfies the following conditional expression (6)
0.5<( Ra+Rb )/( Ra−Rb )<1.2 (6)
where,
Ra denotes a radius of curvature of an image-side surface of the single lens having a positive refracting power, and
Rb denotes a radius of curvature of an object-side surface of the cemented lens.
6. The image forming optical system according to claim 1 , wherein a surface on the object side of a lens positioned nearest to the object side in the second lens group is a concave surface.
7. An electronic image pickup apparatus comprising:
an image forming optical system described in claim 1 ; and
an electronic image pickup element.Cited by (0)
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